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Old 12-24-2011, 04:39 PM   #1
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Default single phase motor / 3 phase starter

Trying to wrap my head around using a 3 phase combo starter to control a 120v motor. In a normal installation, doesn't the starter use two of the 3 legs to power the coil? How could this be accomplished with only a ungrounded and grounded conductor? The engineer made it work on paper! Oh, and Merry Christmas fellas

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Old 12-24-2011, 05:02 PM   #2
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Order the contactor with a 120 volt coil.

You could run both legs of the circuit through the contactor or just the hot and pick up the neutral for the coil by just splicing onto it.

This is pretty straight forward stuff unless I am missing something.

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Old 12-24-2011, 05:11 PM   #3
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I wish it was as straitforward for my mind. This has been a good job for me to be on, as I don't have much experience with motors and controls. The starters were ordered as part of a package, I don't believe the coils are 120v, I assumed they were a lower voltage. But you know what happens when you assume
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Old 12-24-2011, 06:08 PM   #4
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Quote:
Originally Posted by electric mike View Post
I wish it was as straitforward for my mind. This has been a good job for me to be on, as I don't have much experience with motors and controls. The starters were ordered as part of a package, I don't believe the coils are 120v, I assumed they were a lower voltage. But you know what happens when you assume
You can get the coils at all sorts of standard voltages, and often times they're interchangeable.

If you can't/don't want to change the coils, then you can get a small control transformer to adjust your motor voltage to whatever coil voltage you need.

EDIT: And you usually don't want to "assume" what the coil voltage is.
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Old 12-24-2011, 06:26 PM   #5
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The starters were ordered as part of a package, I don't believe the coils are 120v, I assumed they were a lower voltage. But you know what happens when you assume
If they were / are a lower voltage they would not be powered directly from two legs of three phase would they?
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Old 12-24-2011, 07:10 PM   #6
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I wish it was as straitforward for my mind. This has been a good job for me to be on, as I don't have much experience with motors and controls. The starters were ordered as part of a package, I don't believe the coils are 120v, I assumed they were a lower voltage. But you know what happens when you assume
its stamped on the coil what voltage it is.
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Old 12-25-2011, 09:22 AM   #7
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If they were / are a lower voltage they would not be powered directly from two legs of three phase would they?
Powered directly was a terrible description by me. I believe two of the incoming line legs feed the primary of a x-former in the starter, and the coil is powered by the secondary. Like I mentioned, this isn't in my wheelhouse. Thanks guys.

edit: may have found a diagram to help on page 35 in the uglys book
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Old 12-25-2011, 10:02 AM   #8
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Be Careful!

What is your voltage feeding the contactor?

3 Phase or single phase?

You said your motor is 120 volt.

No Magic Smoke PLEASE!

This should be a very simple connection.

Three phase contactor.-----

Just use one leg, unless you want to break the neutral too!

Think of the contactor as a switch, activated by a solenoid coil.
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Old 12-25-2011, 10:22 AM   #9
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Be Careful!

What is your voltage feeding the contactor?

3 Phase or single phase?

You said your motor is 120 volt.

No Magic Smoke PLEASE!

This should be a very simple connection.

Three phase contactor.-----

Just use one leg, unless you want to break the neutral too!

Think of the contactor as a switch, activated by a solenoid coil.
Keeping the magic smoke in is always priority one! The incoming volts are 120. This is where i get lost, how can 120 control the coil when it appears on the starter to be fed by two hots, no neutral? What i don't have in front of me is the voltage of the coil. Will get more info from the foreman next week. Thanks again guys, merry christmas!
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Old 12-25-2011, 11:32 AM   #10
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Keeping the magic smoke in is always priority one! The incoming volts are 120. This is where i get lost, how can 120 control the coil when it appears on the starter to be fed by two hots, no neutral? What i don't have in front of me is the voltage of the coil. Will get more info from the foreman next week. Thanks again guys, merry christmas!
Yes, find out the voltage of the primary but it sounds like it may be too high for your application and you need to switch it out with a 120 volt.
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Old 12-25-2011, 12:14 PM   #11
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I believe two of the incoming line legs feed the primary of a x-former in the starter, and the coil is powered by the secondary.
IF the coil is 120vac.

Eliminate the control xfmr.

Pick the wiring up after the xfmr.

Make sure to remove bonding jumper.(if present)
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Old 12-25-2011, 10:15 PM   #12
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All NEMA combination starters come standard with a fusible disconnect, motor starter, overload relay and optional control transformer.
In the drawing below a transformer is not used. Two legs of the supply are used for control. In your case it will be the grounded conductor and the ungrounded conductor.
To use the power input as the control voltage, the starter coil and any pilot lights must be 120 volts.
If the starter coil is not the same voltage as the source (input) voltage you will need a transformer.
Just isolate the transformer power away from the source power.
I hope the drawing will help.

I would like to see your engineers drawing. Maybe you should be using it.
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Old 12-25-2011, 10:52 PM   #13
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FWIW- if there will be a good many starters off a common control power source, consider powering the coils at 24V instead of from a single pole breaker in the lighting panel. That way, you can at least dump the line side power to the starter line side terminals and compliantly work inside the starter can without PPE and without dumping control power to all the motor starters.

You run into this puzzle a lot more on old MCC's. You PPE up, rack out the bucket, only to find that the control power is still 120V or 240V, and you still need some level of PPE on anyhow. Newer installs typically have 24v control power which, of course, is less than the 50v threshold for needing PPE.
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Old 12-25-2011, 11:28 PM   #14
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Quote:
Originally Posted by John Valdes
All NEMA combination starters come standard with a fusible disconnect, motor starter, overload relay and optional control transformer.
In the drawing below a transformer is not used. Two legs of the supply are used for control. In your case it will be the grounded conductor and the ungrounded conductor.
To use the power input as the control voltage, the starter coil and any pilot lights must be 120 volts.
If the starter coil is not the same voltage as the source (input) voltage you will need a transformer.
Just isolate the transformer power away from the source power.
I hope the drawing will help.

I would like to see your engineers drawing. Maybe you should be using it.
A standard square D 8538 combination starter comes as a disconnect and contacter with an o/l block. That's it, everything else is an option. They will only question about the coil voltage before they ship.
You need to tell them if a transformer is needed, if you want a h-o-a, start-stop, fused, breaker,, ect..
If you don't. Tell them they will ship with MTW from the disconnect to the contactor block. They will size that wire based on max amperage rating of your contactor.
It comes in a NEMA 1 enclosure.
You also need to specify if you want a factory build, if not the options just come in boxes.
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Old 12-26-2011, 01:19 PM   #15
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A standard square D 8538 combination starter comes as a disconnect and contacter with an o/l block. That's it, everything else is an option. They will only question about the coil voltage before they ship.
You need to tell them if a transformer is needed, if you want a h-o-a, start-stop, fused, breaker,, ect..
If you don't. Tell them they will ship with MTW from the disconnect to the contactor block. They will size that wire based on max amperage rating of your contactor.
It comes in a NEMA 1 enclosure.
You also need to specify if you want a factory build, if not the options just come in boxes.
Right. A combination starter by definition is a disconnect and a starter in one enclosure. Everything else including coil (if used) voltage must be specified by the buyer.
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Old 12-28-2011, 07:01 PM   #16
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Got answers today, as always everyone here pretty much nailed it.

Quote:
Originally Posted by John Valdes View Post

I would like to see your engineers drawing. Maybe you should be using it.

There were only our original prints, called for a 480v motor ran thru a combo starter. Motor showed up to site 120v, RFI said re-route conduit from 480 panel to 120 panel and use same starter.


Quote:
Originally Posted by Awg-Dawg View Post
IF the coil is 120vac.

Eliminate the control xfmr.

Pick the wiring up after the xfmr.

Make sure to remove bonding jumper.(if present)
Quote:
Originally Posted by BBQ View Post
Order the contactor with a 120 volt coil.

You could run both legs of the circuit through the contactor or just the hot and pick up the neutral for the coil by just splicing onto it.

This is pretty straight forward stuff unless I am missing something.
Yep and yep, the coil was 120v so we bypassed control x-former and all was right in the world again. Thanks for helping a construction grunt in his quest to become more than just an installer

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